1. Field of the Invention
The present invention relates to tool manipulation apparatus which permits the remote manipulation of tools with respect to an object to be worked on. The invention has particular application to apparatus for cleaning debris from the fuel assemblies of a pressurized water nuclear reactor.
2. Description of the Prior Art
Conventional pressurized water nuclear reactor fuel assemblies comprise a plurality of elongated fuel rods and control guide thimble tubes held in an organized array by grids spaced along the fuel assembly length. Top and bottom nozzles at opposite ends of the fuel assembly are secured to the thimble tubes, which extend above and below the ends of the fuel rods. The spacing between the fuel rods is relatively small, typically less than 1/4 inch, and during installation and operation, the small spaces between the grid straps and the fuel rods acts as a filter which serves to trap debris carried in the primary coolant. This debris has been found to include metal chips, pieces of wire, and other unidentified metallic fragments, and usually becomes lodged between the first grid of the fuel assembly and the bottom nozzle adapter plate.
It has been found that such fuel assemblies have experienced a relatively significant number of cladding failures, i.e., leaking fuel rods, caused in part by the accumulation of debris. Once the debris is trapped, coolant flow can cause the debris to vibrate against the fuel rod and fret a hole in the cladding. Accordingly, it is necessary to remove such debris when it accumulates in the fuel assembly.
Heretofore, this debris removal operation has been effected manually. More specifically, the fuel assembly is suspended under water, such as in a spent fuel pool. Workmen stationed above the pool then manually attempt to remove debris, utilizing tools on the end of long poles or rods which are manually extended down to the desired position on the fuel assembly. Remote video cameras may be used to assist this operation, but it is still an extremely time consuming and difficult procedure, which depends entirely on the skill of the workmen. The changing of tools requires complete withdrawal of the tool and rod from the pool. Also, the manual procedure involves considerable man-rem exposure. Furthermore, there is considerable risk of damage to the fuel assembly, since it is extremely difficult to judge the force being applied to the fuel assembly when the tool comes in contact therewith, not to mention the difficulty of accurately positioning a tool manually at a distance of about 30 feet under water.